Herbicides are very important chemicals for saving weed-controlling labors and improving the yield of agricultural and horticultural crops and have been therefore aggressively studied and developed for many years, and a diversity of herbicides have now been put to practical use. Today, however, it is still desired to develop novel chemicals having excellent herbicidal efficacy, particularly chemicals which can selectively control target weeds alone at a low dosage without causing phytotoxicity on crops.
During the time of planting corn, etc., a triazine-based herbicide such as atrazine and acid anilide-based herbicides such as alachlor and metolachlor have been conventionally used. However, atrazine shows low efficacy to gramineous weeds, and on the other hand, alachlor and metolachlor show low efficacy to broad-leaved weeds. It is therefore difficult at present to control gramineous weeds and broad-leaved weeds together simultaneously with a single herbicide. Further, the above herbicides are undesirable in view of an environmental problem due to their high dosage requirement.
It is-known that in paddy land, a variety of weeds, annual gramineous weeds such as barnyardgrass, annual cyperaceous weeds such as umbrella plant, annual broad-leaved weeds such as monochoria and toothcup and perennial weeds such as sagitaria pygmaea, pondweed, oriental water plantain, bulrush, needle spikerush, serotinus, water chestnut, arrowhead and dropwort grow together with paddy rice, and in rice cultivation, it is very important to effectively control these weeds at a low dosage in view of environmental pollution without causing phytotoxicity on paddy rice. Generally, it is known that chemicals having high herbicidal efficacy on barnyardgrass are liable to cause phytotoxicity on paddy rice, and it is a particularly important subject to develop a chemical which has high herbicidal efficacy on barnyardgrass as a gramineous weed and has excellent inter-genus selectivity between paddy rice and barnyardgrass.
Meanwhile, it is known that specific 4-benzoylpyrazoles have herbicidal efficacy (JP-A-63-122672, JP-A-63-122673, JP-A-63-170365, JP-A-1-52759, JP-A-2-173 and JP-A-2-288866), and pyrazolate of the following chemical formula is among herbicides commercially available at present. ##STR1##
Further, a compound (A), the typical example of 4-benzoylpyrazole derivatives disclosed in the above publications, has the following chemical formula (Compound No. 35 in JP-A-2-173).
Compound (A): Compound No. 35 disclosed in JP-A-2-173 ##STR2##
The above 4-benzoylpyrazole derivatives have herbicidal activity, while their herbicidal activity is practically insufficient. In particular, their herbicidal activity to gramineous weeds such as barnyardgrass and green foxtail is very poor. When they are used as a herbicide for controlling weeds in paddy land, they may cause phytotoxicity on paddy rice since they have poor selectivity between paddy rice and gramineous weeds.
The present inventors have therefore proposed pyrazole derivatives having a thiochroman ring and have filed patent applications directed thereto (JP-A-4-185526 and International Laid-open Patent Publication WO93/18031). Typical examples (B) and (C) of the compounds disclosed in the specifications of the above prior applications are as follows.
Compound (B): Compound No. 66 disclosed in International Laid-open Patent Publication WO93/18031 ##STR3##
Compound (C): Compound No. b-3 disclosed in JP-A-4-185526 ##STR4##
The above compounds have high herbicidal activity, while they still have room for improvement in view of safety to paddy rice.
The present invention has been made in view of the above circumstances, and the object thereof is to provide a pyrazole derivative which can control a broad range of upland weeds and paddy landweeds, particularly barnyardgrass in paddy land, at a low dosage without causing phytotoxicity on crops such as corn, paddy rice, etc., a herbicide containing the same, and an intermediate for obtaining the pyrazole derivative.